1. Field of the Invention
The present invention relates to a reflective optical sensor having a light emitting element to irradiate a target object with a light beam and a light receiving element to receive the light beam reflected by the target object and to an image forming device such as a copier, printer, or facsimile machine incorporating such an optical sensor.
2. Description of the Related Art
In an electrophotographic image forming device such as a copier, printer, or facsimile machine, toner images are generally formed from electrostatic latent images on photoreceptor drums by attaching toner to the electrostatic latent images, and transferred and fused on a paper material for outputs.
To obtain good toner images with proper toner density, the device includes an optical sensor to irradiate a toner patch on a photoreceptor drum or an intermediate transfer belt and calculate the density of the toner patch from the amount of light reflected by the toner patch. The device adjusts the image density to a proper value based on the calculated density by controlling a charge bias or a develop bias, for example.
Japanese Patent Application Publication No. 2007-13050 discloses a typical reflective optical sensor or photosensor which includes a light emitting element to irradiate the toner patch as a target object with a light beam and a light receiving element to receive the light beam reflected by the toner patch.
There may be a case that a part of the light beam from the light emitting element is reflected by the surface of a circuit board and enters the light receiving element. This reflective optical sensor includes a light shielding wall between the light emitting element and light receiving element, to prevent the reflected light beam from leaking as ambient light to the light receiving element. The incidence of ambient light on the light receiving element causes a decrease in the accuracy of detection of a toner density.
In this reflective optical sensor, a groove is formed on the circuit board surface between the light emitting and receiving elements, into which the light shielding wall is fitted, for the purpose of preventing the reflected light beam from leaking through a gap between the bottom surface of the light shielding wall and the circuit board. To fit the light shielding wall into the groove without a play, the circuit board needs to be cut by a router to form the shape of the groove precisely. This increases the production time and costs for prevention of light leakage.